Have you ever heard of such a thing?

I’m all kinds of emotional right now. I went in today to confirm an empty gestational sac they saw last week at what was supposed to be 11 weeks. Today they saw a yolk sac and fetal pole looking to be about 6 weeks. They still didn’t see a heartbeat but now I have to go back next week to make sure. I literally don’t know what to do or think. How is this even possible? I saw the ultrasound last week and it was definitely empty. Here is the picture from today. I’m trying not to get my hopes up but I’m in shock.